The present invention relates to an endless multilayer fabric used for densifying paper materials, and a production process for making the fabric. In operation, the fabric removes ink particles and ash content from aqueous solutions of regenerated paper materials derived from waste papers such as newspapers obtained by deinking, deashing and other means.
Japanese Laid-Open Patent No. 2-14090/1990 is an example of a known endless fabric, in which protrusions are sewn in both ends of the width direction of fabric.
Densification of paper materials such as waste papers differs from paper manufacturing; that is, pulp materials are not uniformly deposited onto a fabric in small increment volume but are discharged under conditions where solid contents are not uniformly dispersed. Thus, in use the fabric is subjected to uneven large loads, and the rotating of endless fabric moves obliquely and sometimes is unwound from the inner roll.
For preventing such phenomena, trials have been made to provide a channel on the inner roll and to provide a guide protrusion engaging the channel in both ends of the width direction of the fabric; however, the end surface of the protrusion in the central part of the fabric cuts in a short period when the fabric runs.
Similar cutting occurs in a case where the side surface of the guide protrusion is contacted to the end surface of the inner roll for preventing the oblique movement without providing the engaging channel on the inner roll.
A known technology disclosed in Japanese Laid-Open Patent No. 2-14090/1990 mentioned above discloses the guide protrusion sewn to the fabric for preventing such cutting. By securing with sewing, the cutting of fabric is moderated to a considerable extent unlike fusion since there is free space between the protrusion and the fabric.
However, the cutting cannot be prevented perfectly and the guide performance disadvantageously deteriorates.
Japanese Laid-Open Patent No.4-361682/1992 discloses a densification endless fabric in which a guide protrusion molded in polyurethane is provided on a bending resistant part filled with polyurethane in trimming parts of an endless fabric woven by plastic monofilament.
While this net is excellent in the guide performance, the fabric has a problem of cutting in the inner end parts of the bending resistant part during use.
A fabric is, generally, woven with warp and weft and is not a rigid body; finishing treatment does not give the whole fabric uniform elongation, tensile strength and rigidity. Thus, revolution of the fabric in an endless conditions makes the fabric move from the more elongated side to the less elongated side. The crimp arrangement on the running surface of fabric makes the fabric move obliquely to one side. Furthermore, insufficient running center adjustment in a device for making the fabric rotate in an endless condition also makes the fabric move to one side.
Oblique fabric movement occurs due to various causes as explained above. The direction of oblique movement is fixed by each fabric and by the device rotating the fabric under an endless condition. If the direction of oblique movement is decided, provision of a guide protrusion in the trimming part of the opposite side is enough; however, the direction of oblique movement is ordinarily unclear until the running, and it is preferable to arrange guide protrusions on both side trimming parts. On the other hand, densification of paper materials such as waste papers is made by feeding a stream containing these onto a fabric or between a fabric and an inner roll. Dehydration is made by compression between the fabric and inner roll or by centrifugal force. Hence, if a heavy material is placed on the fabric or between the fabric and inner roll, the tension changes, and the oblique movement is accelerated. If the oblique movement is excessive, the fabric gets out of the inner roll.
When a guide protrusion is arranged in the end parts of the width direction of a fabric for guiding to engage with a channel provided in a inner roll and the channel depth is nearly equal to the guide protrusion, the inner surface of guide protrusion contacts the inner wall surface of the channel in the fabric portion that contacts the inner roll. However, the fabric tends to move more inwardly and the guide protrusion is pulled inwardly and led to go away from the channel whereby the outer side of the guide protrusion is raised and the fabric bends near the inner surface of the guide protrusion.
On the other hand, when the fabric moves outwardly against the guide protrusion, the outer surface of the guide protrusion contacts the outer surface of the outer wall surface of the channel. However, the fabric tends to move more outwardly and the guide protrusion is pushed outwardly and led to go away from the channel whereby the inner side of the guide protrusion is raised and the fabric bends by being pushed to the guide protrusion. When the fabric leaves from the inner roller, the bending is relieved. This bending movement is repeated and thereby the fabric is cut near the inner surface of the guide protrusion.
When fastening of the guide protrusion to the fabric is loosened and free space is provided for allowing small movement of the guide protrusion in the occasion the fabric is pushed to the guide protrusion, the bending of the fabric is moderated to some extent; however the cutting cannot be prevented. In addition, loose fastening of the guide protrusion decreases the guide performance; thereby the tendency of going away from the inner roller channel is disadvantageously increased. The protrusion may be provided at one end of the width direction or may be provided at both ends. Of course, the guide protrusion may be guided in contact with the end surface of the inner roller. In such a case, the guide protrusions are conveniently at both ends of the width direction of the fabric. When the fabric is spread and set, the guide protrusions are not directly spread and set on to the inner roller and the direct tension is not applied. The tension in the guide protrusion is smaller than in the fabric. Thus, the guide protrusion therefore bends to the center axis direction of the inner roller at the part of the fabric contacting to the inner roller. Hence, the fabric bends near the inner surface of the guide protrusion; when the fabric is left from the inner roller, the bending is moderated to mild bending. When this bending is repeated continuously, the fabric near the guide protrusion is abraded at the shoulder part of the inner roller by the bending of the guide protrusion to the direction of center axis of the inner roller as mentioned above, and the fabric is cut near the inner surface of the guide protrusion. In addition, when an inner roller having a deeper channel than the size of the guide protrusion, similar cutting occurs.
The present invention is to provide a fabric that has good guide performance and strong resistance to cutting thereby overcoming the defects mentioned above and to provide a process for densifying paper materials such as waste papers using this fabric.